Never gonna give EU up, never gonna let you down... er

At some point in the next few years we will be in a post-Brexit world, and the UK will have regained complete control of its borders. Or maybe not. At this juncture, it's worth taking a long hard look at how that might work.

Spoiler: it won't. And that's because of two things, law and logistics.

Those immediately affected by the UK reclaiming its borders are non-UK EEA (European Economic Area) citizens living in the UK. That is the EU plus Iceland, Lichtenstein and Norway. Switzerland is not a member of the EU or the EEA, but its citizens have similar freedom of movement rights. In the interests of brevity, we'll use EU citizen as shorthand for all this – it's not entirely accurate, but it's near enough.

There are variously estimated to be 2.9 million, 3.3 million, or 3.5 million EU citizens in the UK. Theresa May's government - and famously the PM herself - have adopted a "no guarantees" posture regarding the status of these, but don't panic, because the status of most of them is pretty much guaranteed, and indeed the government has guaranteed it. Albeit quietly.

Permanent residence, freedom of movement and EU

Many EU citizens living in the UK already do have the right to stay. EU citizens currently have the right to freedom of movement within the EU, to work and stay in another EU country, to stay there after employment has finished, and to have equal treatment with nationals. This will not apply once the UK has left, but those EU citizens who've been in the UK for five years automatically get permanent residence status, provided they've been in employment, self-sufficient or studying. They can apply for a certificate of permanent residence after this, and they now need that for naturalisation/citizenship, but it's the five years that gives them residence, not the certificate.

The government confirmed this in a statement issued recently: "EU nationals who have lived continuously and lawfully in the UK for at least 5 years automatically have a permanent right to reside. This means that they have a right to live in the UK permanently, in accordance with EU law. There is no requirement to register for documentation to confirm this status."

In evidence to the Committee, Immigration Minister James Brokenshire said that the right to remain could not be taken away: "as a matter of law it would be virtually impossible - through the ECHR, article 8 [of the European Convention on Human Rights] and anything else - to take that away from them."

Because this is EU law, British citizens in the rest of the EU have similar rights. But although the rights are automatic provided you qualify, when you apply for a UK certificate of permanent residence you do have to prove you qualify. Post-Brexit, EU citizens will certainly need some form of proof of their right of residence and right to work, but we can't count on that being provided via the current permanent residence certificate route.

In a recently published report, Migration Observatory says that each year the Home Office has been processing an average of 25,500 permanent residence certificate applications from EEA citizens and their family members, and these applications are frequently made in order to gain right of residence for a non-EEA spouse. By the first quarter of this year, the report says that 64 per cent, or 2.3 million of the 3.5 million EEA citizens in the UK qualified for permanent residence. If we assume that it will take two years to leave the EU after Article 50 is triggered, another 435,000 (12 per cent) will have qualified. The precise number will of course depend on when Article 50 is triggered - the consensus was that we'd likely do this in January 2017, but later in the year, possibly as late as December, now seems possible.

Hang on, that's a truckload of paperwork...

Assuming January 2017 and therefore a January 2019 exit, between now and then – if we stick with the permanent residence certificate approach – we've got 2.7 million applications to process. The application form is 85 pages long and requires paperwork about your work and travel arrangements for the five-year period. While it must surely be possible to shorten the form, if you're going to separate these people from those who haven't been in the UK long enough to establish residence, those who arrive between the referendum and exit, and those who've got a fake EU ID card, you're going to need that paperwork, and you're going to need people to check it. Essentially, this is what controlling your own borders entails.

At present throughput, says Migration Observatory, it would take 140 years to process everybody. Which is obviously silly, but if the UK is to be in a position to control its borders on exit, then EEA citizens will have to be processed in a period of just over two years. Or the UK will have to take a pretty relaxed approach to residence for EEA citizens.

Which, incidentally, is what we do right now. You can however begin to see why despite already qualifying for permanent residence these people could be a kind of bargaining chip.

What about all the Brits abroad?

UK citizens elsewhere in the EU have precisely the same rights as EU citizens in the UK, and both groups are protected by the same EU law and the ECHR backstop if necessary. But if there is no EU-UK agreement on how they are treated after Brexit, different countries will inevitably treat them differently - rules on calculating length of residence and dealing with breaks in employment could vary, for example.

This is probably more important for UK citizens in the EU than vice-versa, as a fair number will be economically inactive (see the Migration Observatory report for how the UK defines this). The UN estimates that there are 1.2 million UK nationals in the rest of the EU, but that seems low, and tends to conflict with the estimates of some EU countries.

An applicant for a UK permanent residence certificate could be unsuccessful if retired or deemed to be economically inactive. In the latter case, earnings have to have achieved a specific threshold, so people in low-paid work don't qualify as economically active, while retired, inactive and students need to have comprehensive health insurance.

Post-Brexit, this may become necessary for everyone, depending on whether or not a health deal is part of the negotiations. Anyone considering a permanent residency application, incidentally, would do well to read the guidance on Colin Yeo's very helpful Free Movement blog.

If we apply the UK's residency rules - or possibly stricter ones - to the UK citizens in the rest of the EU without a prior agreement, you could wind up with a lot of retired and downshifted people with no right to remain, their status possibly dependent on who gets elected next time.

So May is right to keep the guarantees to a minimum until she's clinched some form of reciprocity, call it a bargaining chip if you like.